Muxless Dual AMD + Xorg 1.14 = blank screen

[Alex Deucher]

On Thu, Sep 26, 2013 at 3:13 PM, Alexander Konotop
<alexander.konotop at gmail.com> wrote:
> Hello, guys :-)
>
> Couldn't someone tell me if it's an issue or it really won't work as
> still unimplemented, or maybe I'm doing smth wrong:
>
> I have an AMD APU + External AMD card (Muxless). here's lspci --vv output for
> them:
>
> 00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Sumo [Radeon HD 6480G] (prog-if 00 [VGA controller])
>         Subsystem: Hewlett-Packard Company Device 168c
>         Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
>         Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
>         Latency: 0, Cache Line Size: 64 bytes
>         Interrupt: pin A routed to IRQ 48
>         Region 0: Memory at b0000000 (32-bit, prefetchable) [size=256M]
>         Region 1: I/O ports at 7000 [size=256]
>         Region 2: Memory at d8100000 (32-bit, non-prefetchable) [size=256K]
>         Expansion ROM at <unassigned> [disabled]
>         Capabilities: <access denied>
>         Kernel driver in use: radeon
> 01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Seymour [Radeon HD 6400M/7400M Series] (prog-if 00 [VGA controller])
>         Subsystem: Hewlett-Packard Company Radeon HD 6470M
>         Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx+
>         Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
>         Latency: 0, Cache Line Size: 64 bytes
>         Interrupt: pin A routed to IRQ 50
>         Region 0: Memory at c0000000 (64-bit, prefetchable) [size=256M]
>         Region 2: Memory at d8000000 (64-bit, non-prefetchable) [size=128K]
>         Region 4: I/O ports at 6000 [size=256]
>         Expansion ROM at d8020000 [disabled] [size=128K]
>         Capabilities: <access denied>
>         Kernel driver in use: radeon
>
>
> I've at first read this page:
> http://xorg.freedesktop.org/wiki/RadeonFeature/
> especially the phrase "X Server 1.14 is required to support rendering and display from different cards"
> and "MOSTLY" at the "Hybrid Graphics/PowerXpress/Enduro" row for my cards.
> and subscribed to this mail list to see any news on Dual Graphics support or bugs.
>
> At second I'we waited for xorg 1.14 to appear in my distro.
>
> At third I've tried to setup my two cards using this post:
> http://forums.linuxmint.com/viewtopic.php?f=49&t=139413
> So I'm using xrandr to switch the PRIME card and it looks like workng at first:
>
> $ glxinfo | egrep "(OpenGL vendor|OpenGL renderer|OpenGL version)"
> OpenGL vendor string: X.Org
> OpenGL renderer string: Gallium 0.4 on AMD SUMO
> OpenGL version string: 3.0 Mesa 9.1.6
>
> $ DRI_PRIME=1 glxinfo | egrep "(OpenGL vendor|OpenGL renderer|OpenGL version)"
> OpenGL vendor string: X.Org
> OpenGL renderer string: Gallium 0.4 on AMD CAICOS
> OpenGL version string: 3.0 Mesa 9.1.6
>
> But if I try to run a fullscreen game specifying DRI_PRIME=1 - it shows blank screen.
> I can write "/quit" in the game's console (being blind) and it really quits - so it's not a hang.
> Sometimes xserver restarts while trying to run a game this way. Syslog and Xorg.0.log are empty.
>
> After that I tried to run non-fullscreen (I've run glxgears). glxgears shows twice more fps but it's window is just black.
>
> So it seems like xrandr asks the xserver to render on a second GPU but it doesn't ask it to use the first GPU to output video.
>
> So maybe I need to configure xorg.conf somehow? I've read somewhere that there's no need to do it if I use xrandr to switch
> and no need to restart Xserver for muxless systems.

On a muxless system, there are often no displays connected to one of
the GPUs so it can only be used for rendering.  You can't force X to
start on that GPU because there are no displays.  You don't need an
xorg config.

> Btw if I restart xserver my xrandr settings will fall back to using APU's GPU as primary.
>
> To start an Xserver I'm using lightdm.

You need to be using a compositing window manager to start with.  See
this page for more info:
http://nouveau.freedesktop.org/wiki/Optimus/

You can probably resize the window to make the display appear.  I
think there may be some damage tracking issues that need to be sorted
out in the xserver, but no one has had a chance to look into them yet.

Alex